This is the final version of the article. Available from the publisher via the DOI in this record. ; Sperm commonly compete within females to fertilize ova, but research has focused on short-term sperm storage: sperm that are maintained in a female for only a few days or weeks before use. In nature, females of many species store sperm for months or years, often during periods of environmental stress, such as cold winters. Here we examine the outcome of sperm competition in the fruit fly Drosophila pseudoobscura, simulating the conditions in which females survive winter. We mated females to two males and then stored the female for up to 120 days at 4°C. We found that the outcome of sperm competition was consistent when sperm from two males was stored for 0, 1 or 30 days, with the last male to mate fathering most of the offspring. However, when females were stored in the cold for 120 days, the last male to mate fathered less than 5% of the offspring. Moreover, when sperm were stored long term the first male fathered almost all offspring even when he carried a meiotic driving sex chromosome that drastically reduces sperm competitive success under short-term storage conditions. This suggests that long-term sperm storage can radically alter the outcome of sperm competition. ; This work was funded by NERC (grants NE/H015604/1 to TP and NE/I0277/11/1 to NW and TP), and a Genetics Society (a Genes and Development Summer Studentship to AC and TP). We thank Rudi Verspoor and Chloe Heys for laboratory assistance. We would also like to thank our reviewers for their excellent and insightful suggestions, which improved this manuscript.